Ever since I started down the path of trying to combine Holmes and Cook, I have been trying to create a megadungeon that would tick off all the boxes I see suggested in a Holmes-style game. To a certain extent, I have accomplished much of what I wanted with my version of the Chateau des Faussesflammes, but the result has been, well, really complex.
As my Gamer ADD has recently returned to Holmes, I have been working on taking some of the ideas I put into practice with the Chateau, but in a much simpler format in order to flesh out the Sample Dungeon found in Holmes.
Here is the basic concept: The dungeon beneath Portown is part of the Mythic Underground. Therefore, it is an NPC unto itself. One of the great dangers of the Mythic Underground is that as an environment, it is hostile to adventurers (as is evidenced by the fact that doors easily open for monsters, but PCs must use Thief Skills, spells or Strength). One way that hostility can express itself is by actually changing.
Under Portown, there are six elements of the dungeon that do not change. One is the entrance and there are five special areas which all play a major part in the backstory of the dungeon itself. I've drawn these up here:
The idea here is that the spaces around these six elements can change on a whim. For my part, I am imagining various factions vying for control of the dungeon. Each faction controls a different version of the dungeon. As each faction's power waxes and wanes, the Mythic Underground exposes different versions of itself to the surface world.
Thus, I can take a piece of tracing paper and draw out different "levels" and place them over my six static elements. Here is a version where I took pieces and parts of the Sample Dungeon of Holmes:
Alternately, I can do this electronically. I purposely used geomorphs to create the five main elements of the dungeon so that it would be possible to create something in Dave's Mapper to drop my main elements into with little effort on my part:
The result is an ever-changing megadungeon with an unlimited number of rooms; however, PCs will always have anchor points of familiarity if they can find those unchanging elements of each version of the dungeon. If they can figure out part of the mechanism of when the dungeon changes, they can also begin to have some control over which version of the dungeon they explore.